//------------------------------
// The fastMavlink library
// (c) OlliW, OlliW42, www.olliw.eu
//------------------------------
// these function are based on the pymavlink-mavgen project
// https://github.com/ArduPilot/pymavlink/tree/master/generator

#pragma once
#ifndef FASTMAVLINK_CRC_H
#define FASTMAVLINK_CRC_H

#include <stdint.h>
#include "../fastmavlink_config.h"


// The MAVLink crc16 is CRC-16/MCRF4XX
// check "123456789" -> 0x6F91
// see https://crcmod.sourceforge.net/crcmod.predefined.html
// see https://crccalc.com/
// https://gist.github.com/aurelj/270bb8af82f65fa645c1

// brute force implementation:
//   *crc ^= data;
//    for (uint16_t i = 0; i < 8; i++) {
//        *crc = (*crc & 1) ? (*crc >> 1) ^ 0x8408 : (*crc >> 1);
//    }
//
// for another implementation see https://gist.github.com/aurelj/270bb8af82f65fa645c1


#define MCRF4XX_INIT_CRC  0xffff


FASTMAVLINK_FUNCTION_DECORATOR void fmav_crc_init(uint16_t* crc)
{
    *crc = MCRF4XX_INIT_CRC;
}


#ifdef FASTMAVLINK_CRC_LOOKUP_TABLE

#ifdef __GNUC__
  #pragma GCC push_options
  #pragma GCC optimize ("O3")
#endif

// generated from https://crccalc.com/
static const uint16_t fmav_crc_table_MCRF4XX[256] = {
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};


FASTMAVLINK_FUNCTION_DECORATOR void fmav_crc_accumulate(uint16_t* crc, uint8_t data)
{
    // one often finds crc = (crc << 8) ^ table[(crc >> 8) ^ data], but we need it differently here
    //*crc = (*crc >> 8) ^ fmav_crc_table_MCRF4XX[(*crc ^ data) & 0xff];
    *crc = (*crc >> 8) ^ fmav_crc_table_MCRF4XX[(uint8_t)(*crc & 0xff) ^ data];
}


FASTMAVLINK_FUNCTION_DECORATOR void fmav_crc_accumulate_buf(uint16_t* crc, const uint8_t* buf, uint16_t len)
{
    while (len--) {
        *crc = (*crc >> 8) ^ fmav_crc_table_MCRF4XX[(uint8_t)(*crc & 0xff) ^ *buf++];
    }
}

#ifdef __GNUC__
  #pragma GCC pop_options
#endif

#else

FASTMAVLINK_FUNCTION_DECORATOR void fmav_crc_accumulate(uint16_t* crc, uint8_t data)
{
    uint8_t tmp;

    tmp = data ^ (uint8_t)(*crc & 0xff);
    tmp ^= (tmp << 4);
    *crc = (*crc >> 8) ^ (tmp << 8) ^ (tmp << 3) ^ (tmp >> 4);
}


FASTMAVLINK_FUNCTION_DECORATOR void fmav_crc_accumulate_buf(uint16_t* crc, const uint8_t* buf, uint16_t len)
{
    while (len--) {
        fmav_crc_accumulate(crc, *buf++);
    }
}

#endif


FASTMAVLINK_FUNCTION_DECORATOR uint16_t fmav_crc_calculate(const uint8_t* buf, uint16_t len)
{
    uint16_t crc;

    fmav_crc_init(&crc);
    while (len--) {
        fmav_crc_accumulate(&crc, *buf++);
    }

    return crc;
}

#endif // FASTMAVLINK_CRC_H


